Did it just start crashing a lot? What has changed that may have caused the stability to be worse? If you need the additional features found in 6.0 and 6.5 including the UI changes, then go for it. But seeing as you are on 5.0, have you looked into 5.x updates to see if that stabelizes things for you>
It's been pretty unstable in general as I've been using it in the last couple months.
Lately it's really bad. My macBook pro is a little wonky and old. I did do a verify and repair permissions recently to try to help the situation. I was told that I might need to uninstall and reinstall Avid.
Since I have the academic version of MC, I have 4 years of free upgrades, which is why I was hoping it might solve my problems. And since it's free, I thought I might as well go for the latest MC. And I'm going to have my IT dept upgrade me to mountain lion, since I don't think MC 6.5 will work on anything lower.
I am on 10.8.2 (10.8.3 is not qualified yet), using 6.5.2 and it's been quite stable overall. If you have the opportunity to move to Mountain Lion (even better with a clean install) and Media Composer upgrade as part of your student license, then I would say go for it.